FIG. 1 is an example of a typical turbocharger. In the turbocharger 1 illustrated, a turbine wheel 2 is connected with a compressor impeller 3 through a shaft 4 which in turn is rotatably supported by a center housing 5. The turbine wheel 2 is received in a turbine housing 6 mounted on the center housing 5 while the compressor impeller 3 is received in a compressor housing 7 mounted on the center housing 5.
Formed in the turbine housing 6 is a turbine scroll 8 so as to surround an outer periphery of the turbine wheel 2. Tangentially introduced into the turbine scroll 8 through an exhaust gas inlet (not shown) is exhaust gas 9 by which the turbine wheel 2 is rotatively driven. The exhaust gas 9 having driven the turbine wheel 2 is axially extracted to an exhaust gas outlet 10.
Formed in the compressor housing 7 is a compressor scroll 11 so as to surround an outer periphery of the compressor impeller 3. By the compressor impeller 3 rotated in accordance with rotation of the turbine wheel 2, sucked air 13 axially taken through an air inlet 12 is compressed and expelled to the compressor scroll 11 and is discharged through the compressor scroll 11 to a compressed air outlet (not shown).
In such turbocharger 1, the shaft 4 for connection of the turbine wheel 2 with the compressor impeller 3 is supported by a floating metal 14 (a bearing portion). Lubricating oil 18 pumped from an oil pan 15 by an oil pump 16 and cooled by an oil cooler 17 is supplied to the floating metal 14 through an oil pathway 19.
The oil pathway 19 comprises an oil supply passage 20 drilled in the center housing 5 and an oil supply pipe 21 routed outside of the center housing 5. The oil supply pipe 21 is connected with the oil supply passage 20 through a joint bolt 22.
The floating metal 14 has an oil throwing mechanism such that the lubricating oil 18 from a gap between the bearing portion and the shaft 4 is flicked out by a centrifugal force of the shaft 4 to an oil discharge port 23 so as to return the oil to the oil pan 15 before leaking of the oil toward the turbine wheel 2 and compressor impeller 3.
In such turbocharger 1, a range of supplied oil amount to the bearing portion on the shaft 4 for connection of the turbine wheel 2 with the compressor impeller 3, which is usable with no fear of oil leakage and seizing, is defined and specified as standard by manufacturers. Since seizing of the bearing portion is to be especially and absolutely prevented, oil supply characteristic is properly set such that the supplied oil amount is reliably within the above-mentioned safely usable range even in a case of a full load where speed-up is attained with an accelerator being fully opened.
There exists, for example, below-mentioned Patent Literature 1 showing general state of the art pertinent to a turbocharger.